Now this is an absolute path and will always stay constant. But we can improve this further. The directory /var/www/project can change , so do we change it everytime ? No instead we make it portable using magic constants like __FILE__ . Take a closer look :

3. Maintain debugging environment in your application

During development we echo database queries , dump variables which are creating problems , and then once the problem is solved , we comment them or erase them. But its a good idea to let everything stay and help in the long run

Code like that is common. Using variables to show status messages has limitations. They cannot be send via redirects (unless you propagate them as GET variables to the next script , which is very silly). In large scripts there might be multiple messages etc.

Best way is to use session to propagate them (even if on same page). For this there has to be a session_start on every page.

5. Make your functions flexible

When adding a single item you use the above function. When adding multiple items , will you create another function ? NO. Just make the function flexible enough to take different kinds of parameters. Have a closer look :

And you will get Headers already send error. Why ? because the "super extra character" has been echoed , and all headers went along with that. Now you start debugging. You may have to waste many hours to find the super extra space.

You can change the output just before sending it to browser if you need to. Think about doing some str_replaces , or may be preg_replaces or may be adding some extra html at the end like profiler/debugger output

Its a bad idea to send output to browser and do php processing at the same time. Have you ever seen a website where there is a Fatal error in the sidebar or in a box in the middle of the screen. You know why that happens ? Because processing and output are being mixed.

9. Set the correct character encoding for a mysql connection

Ever faced a problem that unicode/utf-8 characters are stored in mysql table correctly , phpmyadmin also shows them correct , but when you fetch them and echo on your page they do not show up correctly. The secret is mysql connection collation.

13. Check if directory is writable before writing any files

Before writing or saving any file , make sure you check that the directory is writable or not , and flash an error message if it is not. This will save you a lot of "debugging" time. When you are working on a linux , permissions have to be dealt with and there would be many many permission issues when directories would not be writable , files would not be readable and so on.

Make sure that your application is as intelligent as possible and reports the most important information in the shortest time.

By doing this you get the accurate information that where is a file write failing and why

14. Change permission of files that your application creates

When working in linux environment , permission handling can waste a lot of your time. Hence whenever your php application creates some files do a chmod over them to ensure they are "accessible" outside. Otherwise for example the files may be created by "php" user and you are working as a different user and the system wont let you access or open the file , and then you have to struggle to get root privileges , change the permissions of the file and so on.

15. Don't check submit button value to check form submission

if($_POST['submit'] == 'Save')
{
//Save the things
}

The above is mostly correct , except when your application is multi-lingual. Then the 'Save' can be many different things. How would you compare then. So do not rely on the value of submit button. Instead use this :

17. Don't use the $_SESSION variable directly

Some simple examples are :

$_SESSION['username'] = $username;
$username = $_SESSION['username'];

But this has a problem. If you are running multiple applications on the same domain , the session variables my conflict. 2 different applications may set the same key name in the session variable. Take for example , a frontend portal , and the backend management application , on the same domain.

One clear benefit you get here is if php has inbuilt functions with similar names , then names will not conflict.
Another perspective , though little advanced is that you can maintain multiple versions of the same class in the same application without any conflict. Its basically encapsulation , nothing else.

19. Bunch of silly tips

Use echo instead of print

Use str_replace instead of preg_replace , unless you need it absolutely

Do not use short tags

Use single quotes instead of double quotes for simple strings

Always remember to do an exit after a header redirect

Never put a function call in a for loop control line.

isset is faster than strlen

Format your code correctly and consistently

Do not drop the brackets of loops or if-else blocks.
Do not code like this :

if($a == true) $a_count++;

Its absolutely a WASTE.

Write

if($a == true)
{
$a_count++;
}

Dont try to make your code shorter by eating up syntax. Rather make your logic shorter.

Use a proper text editor which has code highlighting. Code highlighting helps to create lesser errors.

20. Process arrays quickly with array_map

Lets say you want to trim all elements of an array. Newbies do it like this :

foreach($arr as $c => $v)
{
$arr[$c] = trim($v);
}

But it can more cleaner with array_map :

$arr = array_map('trim' , $arr);

This will apply trim on all elements of the array $arr. Another similar function is array_walk. Check out the
documentation on these to know more.

21. Validate data with php filters

Have you been using to regex to validate values like email , ip address etc. Yes everybody had been doing that. Now lets
try something different, called filters.

The php filter extension provides simple way to validate or check values as being a valid 'something'.

22. Force type checking

$amount = intval( $_GET['amount'] );
$rate = (int) $_GET['rate'];

Its a good habit.

23. Write Php errors to file using set_error_handler()

set_error_handler() can be used to set a custom error handler. A good idea would be write some important errors in a file for logging purpose

24. Handle large arrays carefully

Large arrays or strings , if a variable is holding something very large in size then handle with care. Common mistake is to create a copy and then run out of memory and get a Fatal Error of Memory size exceeded :

So it can be seen that in the 3rd copy which was by reference memory was saved. Otherwise in all plain copies memory is used up more and more.

25. Use a single database connection, throughout the script

Make sure that you use a single connection to your database throughout your script. Open a connection right in the beginning and use it till the end , and close it at the end. Do not open connections inside functions like this :

The above example shows how to insert data in a database, without actually having to write INSERT statements. The function insert_record takes care of escaping data as well. A big advantage here is that since the data is being prepared as a php array, any syntax mistake is caught instantly (by the php interpreter ofcourse).

This function can be part of a database class, and callable like this $db->insert_record(). Similar functions can be written for update, select, delete as well. Should be a good practise.

27. Cache database generated content to static files

Pages that are generated by fetching content from the database like cms etc, can be cached. It means that once generated, a copy of it can be writted to file. Next time the same page is requested, then fetch it from the cache directory, dont query the database again.

Benefits :

Save php processing to generate the page , hence faster execution

Lesser database queries means lesser load on mysql database

28. Store sessions in database

File based sessions have many limitation. Applications using file based sessions cannot scale to multiple servers, since files are stored on a single server. But database can be access from multiple servers hence the the problem is solved there. Also on shared hosting, the session files reside in the tmp directory, which is readable by other accounts. This can be a security issue.

Storing session in database makes many other things easier like:

Restrict concurrent logins from same username. Same username cannot log in from 2 different places at same time

It is important to note that error_reporting should never be set to 0 on production machines. Atleast E_FATALs have to be known. Just switch off the display using the display_errors directive. If error_reporting is set to 0, errors wont be raised at all keeping all problems in the dark.

After the display is switched off, the errors should be logged to a file for later analysis. This can be done inside the script using init_set.

1. The path '/path/to/errors.txt' should be writable by the web server for errors to be logged there.

2. A separate error file is specified , otherwise all logs would go inside the apache/web server error log and get mixed up with other apache errors.

3. Also since it is being setup in the current application , the error log will contain the errors of only the current application (there may be other applications running on the webserver).

4. The path can be somewhere inside the directory of the current application as well , so that the system directories like /var/log dont have to searched.

5. Dont set error_reporting to 0. It will not log anything then.

Alternatively set_error_handler should be used to set a custom user written function as the error handler. That particular function, for example can log all errors to a file.

Set 'display_errors=On' in php.ini on development machine

On development machine its important to enable display_errors right in the php.ini (and not rely on ini_set)
This is because any compile time fatal errors will now allow ini_set to execute , hence no error display
and a blank WHITE page.

Similarly when they are On in php.ini , switching it off in a script that has fatal errors will not work.

Set 'display_errors=Off' in php.ini on production machine

Do not rely on init_set('display_errors' , 0); simply because it will not get executed if any compile time fatal errors come in the script , and errors will be displayed right away.

32. Be aware of platform architecture

The length of integers is different on 32 and 64 bit architectures. So functions like strtotime give different results.

But on a 32 bit machine all of them would give bool(false). Check here for more.

What would happen if an integer is left shifted more than 32 bits ? the result would be different on different machines.

33. Dont rely on set_time_limit too much

If you are limiting the maximum run-time of a script , by doing this :

set_time_limit(30);
//Rest of the code

It may not always work. Any execution that happens outside the script via system calls/os functions like socket operations, database operations etc. will not be under control of set_time_limit.

So if a database operation takes lot of time or "hangs" then the script will not stop. Dont be surprised then. Make better strategies to handle the run-time.

34. Make a portable function for executing shell commands

system , exec , passthru , shell_exec are the 4 functions that are available to execute system commands. Each has a slightly different behaviour. But the problem is that when you are working on shared hosting environments some of the functions are selectively disabled. Most newbie programmers tend to first find out which function is enabled and then use it.

The above function will execute the shell command using whichever function is available , keeping your code consistent.

35. Localize your application

Format dates and numbers properly. Show the time according to timezone of the user.
Check here to learn more.

36. Use a profiler like xdebug if you need to

Profilers are used to generate reports that show the time is taken by different parts of the code to execute. When writing large application where lots of libraries and other resources are working to do a cetain task, speed might be an important aspect to optimise.

Use profilers to check how your code is performing in terms of speed. Check out xdebug and webgrind.

37. Use plenty of external libraries

An application often needs more than what can be coded with basic php. Like generating pdf files, processing images, sending emails, generating graphs and documents etc. And there are lots of libraries out there for doing these things quickly and easily.

Few popular libraries are :

mPDF - Generate pdf documents, by converting html to pdf beautifully.

PHPExcel - Read and write Excel files

PhpMailer - Send html emails with attachments easily

pChart - Generate graphs in php

38. Have a look at phpbench for some micro-optimisation stats

If you really want to achieve optimisation at the level of microtime then check phpbench ... it has some benchmarks for various syntax variations that can create significant difference.

39. Use an MVC framework

Its time to start using an MVC (Model view controller) framework like codeigniter. MVC does not make your code object oriented rightaway. The first thing they do is separate the php code from html code.

Clean separation of php and html code. Good for team work, when designers and coders are working together.

Functions and functionalities are organised in classes making maintenance easy.

Lots of tips, techniques, hacks are already implemented in the framework

40. Read the comments on the php documentation website

The php documentation website has entries for each function, class and their methods. All those individual pages have got lots of user comments below them that contain a whole lot of valuable information from the community.

41. Go to the IRC channel to ask

The irc channel #php is the best place online to ask about php related things. Although there are lots of blogs, forums out there and even more coming up everyday, still when a specific problem arises the solution might not be available there. Then irc is the place to ask. And its totally free!!

42. Read open source code

Reading other open source applications is always a good idea to improve own skills if you have not already. Things to learn are techniques, coding style, comment style, organisation and naming of files etc.

The first open source thing that I read was the codeigniter framework. Its easy to developers to use, as well as easy to look inside. Here are a few more

43. Develop on Linux

If you are already developing on windows, then you might give Linux a try. My favorite is ubuntu. Although this is just an opinion but still I strongly feel that for development linux is a much better environment.

Php applications are mostly deployed on linux (LAMP) environments. Therefore, developing in a similar environment helps to produce a robust application faster.

Most of the development tools can be very easily installed from synaptic package manager in Ubuntu. Plus they need very little configuration to setup and run. And the best thing is, that they all are free.